The present invention relates, in general, to zener diodes and, more particularly to mesa zener diodes and the manufacture thereof.
Various types of Zener diodes are known in the art. These devices are designed to go into non-destructive Zener, avalanche, breakdown at particular voltages. As used herein, the term "Zener" or "Zener diode" is intended to encompass all such voltage reference behavior devices, irrespective of the particular breakdown mechanism which gives rise to the voltage reference behavior.
In general, Zener diodes consist of a p-n junction formed from two oppositely doped semiconductor regions having carefully controlled dopant concentration and distribution. For Zener diodes with minimum breakdown voltage, i.e. about 1.8 volts, the p and n regions must both be very highly doped, typically in the range of 10.sup.19 to 10.sup.21 per cm.sup.3, and the junction must be abrupt. This requires a very steep doping profile. In the prior art, alloying has been a preferred method of fabricating Zener diodes in the voltage range of 1.8 to about 10 volts.
The Zener voltage may be increased by reducing the doping, first on one side of the p-n junction, for voltages in the range 1.8 to about 10 volts, and then on both sides of the p-n junction for voltages approximately in the range 10 to 200 volts. Diffusion has been a preferred method for fabricating Zener diodes which operate in the range of about 10 to 200 volts. Diodes having voltages around 10 volts may be fabricated by either method.
The various methods of manufacturing Zener diodes generally utilize a diffusion step to form a portion of the Zener, along with a getter to remove various defects and impurities from the p-n junction. These processing functions have associated processing steps that attribute to the final cost of the devices.
Accordingly, it is an object of the present invention to provide means and methods for manufacture of Zener diodes that overcome the above deficiencies.
It is another object of the present invention to provide means and methods for the manufacture of Zener diodes that do not require diffusion.
It is a further object of the present invention to provide means and methods for manufacture of Zener diodes that do not require a getter process.
It is still a further object of the present invention to provide means and methods for manufacture of Zener diodes that have fewer processing steps and are more economical to produce.